1. Field of the Invention
The present invention generally relates to optical disk units, and more particularly to an optical disk unit for recording information on an optical disk by using a light beam.
2. Description of the Related Art
Conventionally, an optical disk unit for a compact disk (CD), a compact disk recordable (CD-R), or a compact disk rewritable (CD-RW) has employed the 3 beam method as a tracking control method.
According to the 3 beam method, a light beam formed of a main beam and two subbeams is projected onto an optical disk, and by receiving reflected light from the optical disk, tracking control is performed at a time of information recording and reproduction.
FIG. 1 is a diagram for illustrating the 3 beam method.
A main beam MB is focused into a spot on a track 101 of an optical disk 100 and is used for information recording and reproduction, and focus control. A subbeam SB1 is focused into a spot that is in a forward direction, or in a direction indicated by arrow C1, from the spot of the main beam MB. The spot of the subbeam SB1 is displaced from the track 101 in the direction of the periphery of the optical disk 100, or in a direction indicated by arrow D1, with respect to the spot of the main beam MB. A subbeam SB2 is focused into a spot that is in a backward direction, or in a direction indicated by arrow C2, from the spot of the main beam MB. The spot of the subbeam SB2 is displaced from the track 101 in the direction of the center of the optical disk 100, or in a direction indicated by arrow D2, with respect to the spot of the main beam MB.
Reflected light of the main beam MB from the optical disk 100 is detected by a 4-part photodetector, and focus control is performed based on a shape of the reflected light. Further, a reproduced signal is detected based on the intensity of the reflected light. Reflected lights of the subbeams SB1 and SB2 from the optical disk 100 are detected, and tracking control is performed based on a difference between the reflected lights.
However, a beam is scattered by flaws and dust on the surface of an optical disk. The light amount of the beam changes as the beam is scattered. Particularly, if a main beam, which has a large amount of light, is scattered to be detected as a subbeam, a subbeam detection signal is greatly influenced so that a subbeam is prevented from being detected with accuracy.
Japanese Patent No. 2578791 and Japanese Laid-Open Patent Application No. 4-345920 disclose measures to reduce the influence of scattered light.
Japanese Patent No. 2578791 discloses a photodetector having a scattered light detector for detecting scattered light provided around a main detector and subdetectors. In this photodetector, the output signal of the scattered light detector is added to that of the main detector so that the output of-the main detector is stabilized.
Japanese Laid-Open Patent Application No. 4-345920 discloses an optical disk unit that prevents tracking from entering in an uncontrollable state by suspending tracking control when scattered light is detected.
On the other hand, in a recording apparatus for a DRAW (Direct Read After Write) optical disk such as a CD-R or CD-RW, pits are formed in a disk at a time of data recording with an output level of a laser higher than that for data reproduction. Therefore, if a laser beam is focused off a track, that is, the off-track of the laser beam is caused, by vibrations caused by an impact during data recording, the laser beam may be projected onto a recorded area to destroy recorded data. Thus, such a recording apparatus includes a mechanism for suspending a recording operation in the case of an off-track during recording. Such a recording apparatus monitors a track error signal, and determines the occurrence of the off-track to suspend a recording operation when the track error signal reaches a predetermined level or higher during tracking.
As described above, a conventional optical disk unit monitors a track error signal based on the off-track of a laser beam, and determines the occurrence of the off-track to suspend a recording operation when the track error signal reaches a predetermined level or higher during tracking. Therefore, if a main beam is scattered by flaws on a disk to be detected by a subbeam detector so that the level of the track error signal becomes higher, a recording operation may be suspended based on a determination that the off-track has been caused. That is, although the off-track of the laser beam is not caused, the determination that the off-track has been caused is made to suspend the recording operation, thus causing an unstable recording operation.
It is a general object of the present invention to provide an optical disk unit in which the above-described disadvantage is eliminated.
A more specific object of the present invention is to provide an optical disk unit in which both stabilization of a recording operation and protection of recorded data are achieved.
The above objects of the present invention are achieved by an optical disk unit for recording information on and reproducing information from a disk recording medium by projecting a light beam thereonto, which optical disk unit includes a signal level detection part detecting a level of a track error signal generated based on reflected light of the light beam from the disk recording medium, a scattered light detection part detecting scattering of the reflected light, and an off-track detection part which detects an off-track of the light beam using detection signals supplied from the signal level detection part and scattered light detection part.
According to the above-described optical disk unit, the detection signals from both signal level detection part and scattered light detection part are employed in detecting the off-track of the light beam so that an information recording operation is prevented from being suspended by mistakenly detecting a flaw on the surface of the optical disk as an off-track. Therefore, both stabilization of a recording operation and protection of recorded data are achieved.
Additionally, the off-track detection part may detect the off-track of the light beam based on the detection signal supplied from the signal level detection part when the scattered light detection part detects no scattering of the reflected light and may be prevented from detecting the off-track of the light beam when said scattered light detection part detects the scattering of the reflected light.
Thereby, the optical disk unit is prevented from detecting the off-track of the light beam when the scattering of the reflected light is detected, that is, when the disk recording medium has a flaw on its surface. Therefore, an information recording operation is prevented from being suspended by mistakenly detecting the flaw on the surface of the optical disk as an off-track. This prevents the recording operation from being suspended by the flaw of the disk recording medium, thus achieving both stabilization of a recording operation and protection of recorded data in the optical disk unit.